1. Field of the Invention
The invention relates to an apparatus and method for measuring a blood pressure. In particular, the method and apparatus according to the invention are capable of eliminating motion artifacts induced by talking, irregular breathing, frequent swallowing, coughing, shaking, and so on motions of a subject.
2. Description of the Prior Art
Blood pressure is a physical phenomena caused from cardiovascular activity.
Because the change in modern diet and lifestyle, it results in increasing the probability of suffering from high blood pressure. Therefore, long-term and regular self-monitoring of blood pressure in hypertensive patient has become an important daily routine because of the hypertension is a chronic disease.
With the progress of science and technology, blood pressure measurement has been developed of is from early invasive blood pressure measurement to current non-invasive blood pressure measurement. The so-called invasive blood pressure measurement is to insert a sensor and a cardiac catheter into a blood vessel to measure the internal pressure of the blood vessel. However, the invasive blood pressure measurement must be practiced with the cooperation of blood catheter surgery. Obviously, the invasive blood pressure measurement is very inconvenient especially for patients need to be measured frequently. Therefore, the development of non-invasive blood pressure measurement is another goal of blood pressure measurement. The non-invasive blood pressure measurement usually uses a mercury sphygmomanometer to measure blood pressure by judging sound during measurement. However, mercury sphygmomanometers may cause environmental pollution. Therefore, in recent years, mercury sphygmomanometers have been gradually phased out over the world, and been replaced by electronic sphygmomanometers.
Most of electronic sphygmomanometers utilize a cuff to be attached to a patient's arm over the brachial artery. The cuff is first inflated to a pressure that is high enough to substantially occlude the brachial artery. The cuff is then deflated slowly. As the pressure of cuff reduces, blood flowing through the brachial artery beneath the cuff increases gradually, and pulse and blood pressure signals enhance gradually.
When the blood flows through the brachial artery accompanying with each contraction of the heart, it imparts a pulsatile motion to the wall of the artery. These pulsatile motions are coupled to the cuff extending over the artery as minute changes in the cuff pressure, which are known as oscillometric pulses. The electronic sphygmomanometer automatically measures and records the amplitude of the oscillometric pulses at a number of cuff pressures. As shown in FIG. 1, after the blood pressure measurement had been completed, a table containing the oscillometric pulse amplitudes recorded at each cuff pressure is obtained.
In theory, the systolic, diastolic, and mean arterial blood pressures can then be determined from the values in the table using experimental definitions of these parameters as a function of the oscillometric pulses amplitudes. For example, as shown in FIG. 2, it is a blood pressure measurement of particular table recording a number of cuff pressures and the oscillometric pulse amplitudes at each cuff pressure. In FIG. 2, the mean arterial blood pressure is determined by the maximum oscillometric pulse amplitude and the cuff pressure measured with the maximum oscillometric pulse amplitude at the same time. The systolic pressure and diastolic pressure are determined experimentally by mean arterial blood pressure of the oscillometric pulse amplitude multiplied respectively by the first ratio and the second ratio.
However, blood pressure measurements are often adversely affected by artifact, generally induced by motions of a subject, such as talking, irregular breathing, frequent swallowing, coughing, shaking, and so on. As shown in FIG. 3, motion-induced artifacts can substantially alter the measured amplitude of oscillometric pulses, and thus introduce inaccuracies in the measurement of the subject's blood pressure.
Accordingly, one aspect of the invention is to provide an apparatus and method for measuring a blood pressure. In particular, the method and apparatus according to the invention are capable of eliminating motion artifacts induced by motions of a subject.
In addition, references point out that effect on aforesaid first ratio and second ratio to determine the systolic pressure and the diastolic pressure includes the arm circumference of subject. Accordingly, another aspect of the invention is to provide an apparatus and method for measuring a blood pressure. In particular, the method and apparatus according to the invention are capable of measuring the arm circumference of subject to accurately determine the first ratio and the second ratio to calculate the systolic pressure and the diastolic pressure.